This invention relates to a manipulator capable of manipulating a tool or other object with one or more rotational degrees of freedom in a spherical coordinate system.
In various applications, it is desirable to be able to pivot a tool or other object about a point in space which is remote from equipment supporting the tool. Such a point in space is sometimes called a virtual pivot point or a remote center of motion. An example of a situation in which it is useful to be able to pivot a tool about a virtual pivot point is in medical procedures. A medical tool often needs to be pivoted about a point in, on, or in proximity to a patient""s body, but it may be undesirable to have support structure for the tool located at the point, since the support structure may introduce contamination into the patient""s body or interfere with the view of or access to the patient by persons performing the medical procedures. A manipulator which can pivot a tool about a virtual pivot point can avoid such disadvantages of support structure.
One known type of manipulator capable of pivoting a tool in proximity to a virtual pivot point employs a parallel linkage to maintain the orientation of a rod-like tool remotely from the actuation point. The parallel linkage is attached to a rotating base assembly or has some other similar rotating structure at the base which allows the tool to be manipulated in two degrees of freedom (DOF) in a spherical coordinate system. An example of such a manipulator is described in U.S. Pat. No. 5,397,323 entitled xe2x80x9cRemote Center-Of-Motion Robot For Surgeryxe2x80x9d. This and other conventional parallel linkage manipulators have the drawback that the virtual pivot point must lie on a rotational axis of two of the links of the linkage. More specifically, the virtual pivot point must lie in the same plane as the rotational axis of the base and must be inline with the distal pivots of the manipulator. The manipulator disclosed in U.S. Pat. No. 5,397,323 only produces an approximate remote center of motion if the tool is mounted in from the distal pivots, since the tool actually sweeps an arc in one plane rather than pivoting around a point.
One disadvantage of these constraints on the location of the virtual pivot point is that it can be difficult to position the manipulator with respect to a patient""s body and other equipment. In particular, the requirement that the virtual pivot lie in the same plane as the rotating structure at the base can cause clearance problems with a patient or with other equipment being used in the medical procedure such as imaging equipment. The clearance problems can require the patient or a person performing a medical procedure to assume an uncomfortable position.
In addition, the requirement that the virtual pivot point be inline with the distal pivots of the manipulator can make conventional parallel linkage manipulators difficult to use in biopsies and other medical procedures performed in conjunction with imaging systems such as computer tomography (CT) equipment, x-ray equipment or magnetic resonance imaging equipment. In a biopsy performed using imaging equipment, a biopsy needle is inserted into a patient""s body while the patient is outside the imaging equipment. The patient is then placed inside the imaging equipment and an image is taken to determine the location of the biopsy needle with respect to the region of the body where the biopsy is to be performed. It is frequently difficult or unsafe for a human operator to adjust the position of the biopsy needle while an image is being taken. For example, there often is a very limited amount of space between the interior of the imaging equipment and the patient""s body. Additionally, the operator could be exposed to harmful radiation from the imaging equipment or the operator could interfere with the imaging process. Thus, each time the position of the biopsy needle has to adjusted, the patient is withdrawn from the imaging equipment and then reintroduced into the imaging equipment after the position of the biopsy needle has been adjusted. Obviously, such a procedure is very time consuming and imprecise.
Recent advances in CT technology have decreased the time to generate an image to the point that near real time video images can be produced. With this technology, a doctor can place a medical tool with high precision, but he must be very close to the radiation source and receives a higher dose of harmful radiation.
One way in which these problems can be addressed is by using a manipulator that is capable of adjusting the position of a needle or object with respect to a patient""s body while imaging is being carried out. However, with conventional parallel linkage manipulators that can produce a remote center of motion, the distal pivots are in the same plane as the image of interest and tend to distort that image. If the tool is offset from the distal pivots of the manipulator, as is the case with the manipulator described in U.S. Pat. No. 5,397,323, the tool will no longer rotate about a true virtual pivot point. Instead, the tool will move in a small arc as the manipulator is swung about.
Accordingly, in view of the foregoing, a general object of the present invention is to provide a manipulator capable of manipulating a tool or other object with two rotational degrees of freedom about a virtual pivot point with fewer constraints on the position of the manipulator relative to the virtual pivot point than with conventional manipulators.
The term link will be used herein to refer to a member which functions as the equivalent of a rigid body when moving parallel to a specific plane. Thus, a link may be a rigid body, or it may comprise a plurality of components which can move together as a single body parallel to the specific plane but which are movable with respect to each other in a plane transverse to the specific plane. For example, in some embodiments, a group of components which function as a parallel linkage for movement parallel to a first plane may function as a single link for movement parallel to a second plane transverse to the first plane.
Two links are considered parallel to each other when a line connecting two rotational axes of one link is parallel to a line connecting two rotational axes of the other link.
The term pivot point will be used to refer to a point at which a link is physically connected to another member for pivoting with respect to the other member about an axis, while the term virtual pivot point will refer to a point in space at which a link can pivot about an axis passing through the virtual pivot point without the link having to be physically supported at the virtual pivot point. Pivot can provide one, two or three degrees of rotational freedom.